The invention relates to a slide-in print unit for a variable format in offset printing, the unit comprising a machine frame within which there is positioned a counter pressure cylinder, rubber blanket cylinder, and plate cylinder, as well as a drive mechanism for the aforementioned cylinders.
Slide-in print units of this type are known and are disclosed, for example, in European patent document EP 1 101 611 A and German patent document DE 199 55 084A. These slide-in units respectively comprise a counter pressure cylinder, a rubber blanket cylinder and a plate cylinder. An endless paper web moves between the rubber blanket cylinder and the counter pressure cylinder. An inking unit installed in the print unit applies ink to the plate cylinder which in turn transfers ink to the rubber blanket cylinder. Changing the print image length with such a slide-in print unit requires the replacement of format sections of the plate cylinder and the rubber blanket cylinder. These format sections have a sleeve-type design and are respectively fitted in an axial direction onto a so-called air shaft. Following the replacement of the format sections, the axial spacing between the cylinders and, as a rule, also between the cylinders and the inking unit must be changed. In addition, the speed of the rubber blanket cylinder and the plate cylinder must be adapted.
The following two embodiments are known from practical operations as drive means for a slide-in print unit of this type.
For one embodiment, the counter pressure cylinder, the rubber blanket cylinder, the plate cylinder, and the inking unit are each provided with a separate drive, for example a separate motor. On the whole, a slide-in print unit of this type therefore has four independent drives. With this print unit, the rubber blanket cylinder and the plate cylinder speeds can be adapted without problems if the print image length changes. However, the costs of producing such a print unit are comparably high because suitable motors are expensive.
With the second embodiment, one drive is provided for driving the complete slide-in print unit, including the format sections and the inking unit. The aforementioned cylinders and the inking unit are thus driven jointly by a single drive. If the print image length is changed, then drive wheels mounted on the aforementioned air shafts must be replaced, so that the circumferences of the partial circles for the drive wheels correspond once more to the print image length. The costs for producing a print unit of this type are comparably low. The disadvantage lies in the long set-up time during a format change because the drive wheels must be replaced, as previously mentioned.